1. Field of the Invention
The present invention relates to a digital single-lens reflex camera, and in particular relates to a digital single-lens reflex camera having an electronic viewfinder which displays moving images, based on image data consecutively output from an image-capturing device, with a display device.
2. Description of the Related Art
Conventionally, still-image image-capturing devices (hereafter referred to as “digital camera”), which are configured so as to carry out image formation of a subject image formed, based on luminous flux entering a photographing optical system made up of multiple lens groups (hereafter referred to as “subject luminous flux”), on the photo-receiving plane of an image-capturing device or the like, such as a CCD (Charge Coupled Device) for example, disposed at a predetermined position, thereby acquiring a desired subject image, and to record the acquired subject image on a predetermined recording medium in a predetermined form such as digital data or the like, have been realized and are in widespread use.
Further, there are such digital cameras which have been realized as single-lens reflex cameras having a movable mirror or penta prism provided retractably as to the optical path of the photographing optical system, and also having an optical viewfinder for obtaining an optical observation image of the subject, and these are also beginning to become commonplace. Further, with such single-lens reflex cameras, lens interchangeable types have also been realized, wherein a lens barrel having a photographing optical system for example and a driving mechanism thereof and so forth within, is formed so as to be detachably mounted to the camera body, such that the user can optionally exchange the lens barrel as necessary.
The series of actions carried out for taking a picture with a conventional digital camera involve mechanical driving actions such as closing down the diaphragm blades of the diaphragm mechanism, being executed in the time period following the user operating the shutter release operation member up to the actual exposure operation with the image-capturing device of the like. That is to say, the exposure operation at the image-capturing device is started only after a predetermined amount of time has elapsed following operation of the shutter release operation member.
In this way, there is a time delay from the point in time that the shutter release operation is performed to the point in time at which the exposure to the image-capturing device starts at the time of performing photography with the digital camera, which is known as a shutter release time lag.
Particularly, in the case of single-lens reflex cameras, there is the need for the additional action of retracting the movable mirror disposed within the optical path of the photographing optical system to the outside of the optical path, in addition to the aforementioned diaphragm mechanism closing actions and so forth, following the shutter release operation. Consequently, there has been the tendency in single-lens reflex cameras for the shutter release time lag to be even longer.
Accordingly, with the current state of the field of conventional generally single-lens reflex cameras, photographers who demand precise shutter release timing deal with the shutter release time lag problem by performing the shutter release operation earlier than the desired timing so as to compensate for the shutter release time lag, which is a highly advanced photographing skill. In light of this, the shutter release time lag of the camera should be always constant.
Conventionally, various proposals have been made for means for suppressing irregularities in shutter release time lag occurring in the various types of cameras, so that the shutter release time lag is always constant, as disclosed in Japanese Unexamined Patent Application Publication No. 2002-199288 and Japanese Unexamined Patent Application Publication No. 6-75266.
The digital camera disclosed in Japanese Unexamined Patent Application Publication No. 2002-199288 has an EEPROM for storing a predetermined time which is equal to or greater than the maximum time necessary for starting driving of the diaphragm mechanism to ending of driving thereof, and effects control so as to execute exposure operations with the image-capturing device after waiting for the predetermined time stored in the EEPROM to elapse following the shutter release operation which instructs starting of the shooting operation.
Also, the single-lens reflex type camera disclosed in Japanese Unexamined Patent Application Publication No. 6-75266 executes the exposing action after waiting for a predetermined amount of time to elapse after a shutter release signal being generated, thereby suppressing changes in the shutter release time lag due to slight changes in the time for retracting the movable mirror, which are in turn due to irregularities in the movable mirror driving mechanism and to effects of the photographing environment.
Now, conventional digital cameras usually have a viewfinder for observing the subject to be photographed at the time of shooting a picture. There are two primary types of viewfinders conventionally used. One is an optical viewfinder made up of an observation optical system, having a configuration like those of conventional so-called film cameras which take pictures with conventional photographing film. The other is the so-called electronic viewfinder device which takes image data consecutively output from the image-capturing device or the like, and displaying a moving image based on the image data using a liquid crystal display device or the like.
On the other hand, conventional digital cameras usually have an image display device such as a liquid crystal display device or the like for reproducing and displaying image data taken by photographing. With a configuration wherein the image display device is used for displaying output data from the image-capturing device or the like, the image display device can be easily used as the aforementioned electronic viewfinder, and accordingly, digital cameras which use the image display device as an electronic viewfinder have been conventionally realized and commonly employed.
In fact, conventional digital cameras which have both an optical viewfinder device and an electronic viewfinder device, allowing the user to switch between the two according to the photographing environment for shooting a subject or according to the preferences of the user, have come into commonplace use.